1. Field of the Invention
The invention relates to a rack bush in a rack and pinion type steering system.
2. Description of Related Art
A steering system in Japanese Patent Application Publication No. 2008-87535 (JP2008-87535A) includes a steering mechanism. The steering mechanism is constituted by a rack and pinion mechanism, and steers steered wheels using a steering torque from a steering shaft. The steering mechanism includes a pinion shaft, a rack shaft, a rack housing, and a tubular rack bush. The pinion shaft has pinion teeth. The rack shaft has rack teeth that engage with the pinion teeth. The rack housing supports the pinion shaft and the rack shaft. The rack bush is held in a holding hole of the rack housing. The rack bush supports the rack shaft so that the rack shaft is slidable in an axial direction thereof.
Japanese Patent Application Publication No. 2004-256029 (JP2004-256029A) describes a rack bush in which a plurality of projections is formed on an inner peripheral surface to inhibit abnormal noise caused by backlash. The rack bush supports the rack shaft through the projections without causing any backlash, and the rack shaft is in point contact with the projections.
The rack bush included in the steering system in JP2008-87535A is interposed between the rack housing and the rack shaft. Therefore, when the rack bush is attached to the rack housing, it is necessary to insert the rack bush into the holding hole while contracting the rack bush so that the diameter of the rack bush is decreased. Therefore, it might be difficult to attach the rack bush to the rack housing depending on a dimensional relation between the rack bush and the holding hole, and a rigidity of the rack bush. In the rack bush in JP2004-256029A, an area of contact between the rack shaft and the projections of the rack bush is small. Therefore, the backlash may occur between the pinion shaft and the rack shaft due to, for example, wear of the projections, and the engagement of the pinion teeth with the rack teeth may be weakened.